A vaporizer is a device that converts liquid into a vapor. Vaporizers are found in a wide variety of industries, such as energy, medicine, perfume, paint, combustion, printing, or other fields where a stream of vapor is desired.
In many instances a vaporizer operates by heating the liquid. Consistency in output of vapor is often of great importance for many applications. For example, fuel cells are becoming increasingly common due to their high rates of efficiency. Central to their operation is the application of a hydrocarbon reformer for catalytically converting a hydrocarbon fuel source into reformate consisting of a gaseous blend of hydrogen, carbon monoxide and perhaps nitrogen and trace components, depending on the type of original fuel.
Generally speaking, to maximize performance of the fuel cell the reformer must supply a continuous supply of reformate. Of course to do this, the reformer must be supplied with a continuous mixture of fuel and other reactants, such as might be provided by a vaporizer.
Most processes require that the delivered vapor stream be steady with no sputtering, surging, or spitting of unvaporized liquid droplets. Furthermore, many applications require that a wide range of steady vapor flow rates be delivered. Vaporization is endothermic and supplying heat may be accomplished by a variety of means of coupling to energy sources at higher temperatures. Vaporizer designs that are stable over a wide range of temperatures are simpler to integrate with these thermal sources and can find utility in a wider range of applications. Many practical applications also require that the vaporizer maintain these advantageous characteristics over long periods of operation.
Whether used for a fuel cell or other application, many liquids, especially hydrocarbon liquids such as diesel, have high boiling points. Although the liquid may be vaporized, there is typically a residue in the form of a varnish-like deposit left behind within the vaporizer. Lower boiling point liquids often have varnish-like deposits as well. These deposits are typically difficult to remove and have a relatively low chemical reactivity. The build up of deposits over time in many cases leads to impaired operation or failure of the vaporizer. Indeed vaporizer lifetime is typically limited by deposit accumulation.
Typically, so as to enhance the vaporization process, the liquid is sprayed as a fine mist into a chamber. Fuel injectors are commonly adapted for use in vaporizers so as to introduce the liquid in the form of a spray as a necessary component in the vaporizing process, see for example U.S. Patent Application 2005/0005918 to Newhouse et al., U.S. Patent Application 2003/0116143 to Armstrong, U.S. Patent Application 2008/0230039 to Weiss et al., U.S. Patent Application 2006/0037308 to Kamijo et al., and U.S. Patent Application 2006/0051637 to Kushibiki at al.
Of course, to provide the liquid as a spray the liquid in general must be pressurized. Pressurizing the liquid may well require additional equipment (such as a pump and/or tank) and or preparation that is not easily provided or incorporated within the system. This is particularly true for portable equipment where size and weight must be minimized.
Though perhaps effective at providing a mist, a fuel injector or other sprayer typically utilizes a small aperture. This small aperture is susceptible to clogging by foreign particles or varnish residue, and given the small nature of the orifice, may provide an unfortunate early point of failure within the vaporizer.
Small passages within a vaporizer have been shown to provide reliable areas for vaporization, but small passages are susceptible to the build up of varnish-like deposits and are easily clogged. Indeed, small passages often result in sputtering and/or surges in the resulting vapor. For applications where the mixture of a gas with a vaporized liquid must be within a specific ratio, such instability in consistency of vaporization is highly undesirable.
Indeed, between the susceptibility to deposit buildup, need for pressurized liquid, and common reliance upon a sprayer element and/or small passages, many vaporizers are unduly complex, potentially unreliable and costly to manufacture and/or maintain.
The susceptibility to deposit build up, need for pressurized liquid, small passages, common reliance on sprayer elements, jetting properties and overall complex arrangement of components make many vaporizers difficult to manufacture, prone to clogging and make cleaning and repair a less than easy process. In addition, the physical size of the components and inherent physics, e.g. free space for droplet spray, and/or attached pressurizing device may limit the size of the vaporizer. These limitations, including that of size, can be problematic when desiring a vaporizer for portable applications and/or where use of a non-pressurized liquid, liquid at a low pressure or overall low pressure drop vaporization is required.
Hence, there is a need for a vaporizer that overcomes one or more of the drawbacks identified above. The present invention satisfies one or more of these needs.